NOTIZEN 691

Kinetics of the Oxidation of Acetaldehyde by they undergo enolisation. Oxidation of aliphatic Manganese(III) Sulphate aldehydes has not received much attention. Kinetics of the oxidation of acetaldehyde was, therefore, undertaken the results of which are reported here. M. S. M urdia, R. S h a n k e r , and G. V. B a k o r e Experimental Chemistry Department, University of Udaipur, India Acetaldehyde (B . D . H., A. R.) was used after (Z. Naturforsch. 29b, 691-693 [1974]; received July 11, 1974) fractionation and its purity checked by its boiling point. Mn(III)-sulphate wras prepared by the method Acetaldehyde, Manganese(III)-sulphate, Activation parameters described by V o g e l 4. The reaction was carried out at 30 + 0.02 °C and was followed spectrophoto- metrically at 520 nm using a Hilger pattern biochem. Oxidation of acetaldehyde with manganese(III)- absorptiometer. The cell tube was surrounded by a sulphate is first order with respect to acetaldehyde and block through which thermostated water was the oxidant. The rate is independent of acidity (2.0 > circulated. [H+] < 5.0 M and initial [Mn(II)]. Formaldehyde is Stoichiometry and product analysis one of the products of oxidation. Activation para­ meters for the reaction have been evaluated. The rate One mole of acetaldehyde consumes 4 moles of the oxidant. Formaldehyde, detected by chromo- of enolisation under similar conditions is less than the tropic acid test6, is one of the products of exidation. rate of oxidation. A mechanism involving a direct Thus, the overall reaction can be represonted as: attack on the aldehyde by Mn(III) has been suggested. CH3CHO + 4 Mn3+ + 2 H20 -> HCHO + HCOOH + 4 Mn2+ + 2 H+ D ru m m o n d and W a t e r s 1 have investigated the oxidation of propionaldehyde and n - butyraldehyde Results and Discussion by manganese(III)-pyrophosphate. They found that oxidation of both these aldehydes are fairly When the concentration of acetaldehyde is in rapid reactions. The rate of oxidation is proportional excess (tenfold or more than [Mn(III)]), the rate at to the concentration of both the aldehydes and that which Mn(III) disappears follows a first order rate of hydrogen ions but is independent of Mn(III)- law up to 60-70% of the reaction. Pseudo first order pyrophosphate. The latter observation has been rate constant, ku is independent of the initial taken as an evidence to suggest that oxidation concentration of Mn(III) ( cf. Table I). The order in proceeds via enolisation. This is further supported [Mn(III)] is, therefore, one. The order with respect by the fact that non-enolisable aldehydes like to aldehyde is also one (Table II). At constant ionic formaldehyde and chloral do not react with Mn(III)- strength, variation of concentration of sulphuric pyrophosphate. acid from 2.0 to 5.0 m does not noticeably affect the Although formaldehyde is unreactive towards rate of oxidation (Table III). Addition of Mn(II) Mn(III)-pyrophosphate it is oxidised by Mn(III)- has no effect on the rate. (Table IV) (cf. K e m p and sulphate under acidic conditions2. It has been W a t e r s 2). The data on the effect of temperature demonstrated earlier by L i t t l e r 3 that Mn(III)- on the rate and activation parameters has been sulphate is able to oxidise ketones much faster than collected in Table V. Rate of enolisation Requests for reprints should be sent to Prof. G. V. D ru m m o n d and W a t e r s 1 have concluded that B a k o r e , Department of Chemistry, University of oxidation of propionaldehyde and n-butyraldehyde Udaipur (M. B . College) Udaipur. 313001, India. by Mn(III)-pyrophosphate is zero order in Mn(III)-

Table I. Variation of rate with initial [Mn(III)].

[CH3CHO]: 5.0 X 10-3 M ; [H2S 0 4]: 2.0 M ; Temperature: 30 °C

[Mn(III)] X 103: (moles/liter) 5.0 6.0 7.0 8.0 10.0 k 4 X 103 (±5.0% ) sec-1: 5.42 5.41 5.38 5.39 5.48

Table II. Variation of rate with initial [acetaldehyde].

[M n(III)]: 5.0 X 10-3 m ; [H2S 0 4]: 2.0 m ; Temperature: 30 °C

[Aldehyde] X 102 (moles/liter): 2.50 3.00 4.00 4.50 k4 X 103 sec-1: 2.75 3.30 4.24 4.72 kj/[aldehyde] (liter mole -1 sec-1) : 0.11 0.11 0.106 0.105 692 NOTIZEN

Table III. Dependence of rate on initial [H 2S 0 4].

[Aldehyde]: 4.50 X 10- 2M; [Mn(III)]: 9.0 X 10- 3 M; Tem p.: 30 °C

[H2S 0 4]* (moles/liter) : 2.0 3.0 3.5 4.0 4.5 5.0 k 4 x 103 sec-1: 3.54 3.30 3.45 3.40 3.50 3.50

* {[H 2S04] + [NaHSOJ} = 5.0m .

Table IV. Dependence of rate on initial [Mn(II)].

[Aldehyde: 3.25 X 10- 2m; [Mn(III)]: 6.60 X 10“ 3 M; Temp.: : 30 °C [H2S 0 4]: 2.0 m ; {[MnS04] + [ZnS04]} : 0.50 M

[Mn(II)] (M): 0.50 0.10 0.20 0.30 0.40 0.50 k4 x 103 sec-1: 3.50 3.55 3.51 3.67 3.50 3.50

Table V. Temperature dependence of rate and activation parameters.

[Aldehyde]: 3.75 x 10-2 m ; [Mn(III)]: 6.0 X 10-3 m ; [H 2S 0 4]: 2.0 M Temperature (°A): 293 298 303 308 JH* JS* (kcals/mole) (e.u.) k4 X 103 sec-1: 1.29 2.30 3.98 6.90 20.1 ± 1.5 + 4.5 ± 5.0

Table VI. Comparison of rate of oxidation with enolisation.

[Aldehyde]: 5.0 X 10- 2m; [Mn(III)]: 5.0 X 10- 3 m; [H2S 0 4]: 2.0 m; Temp.: 30 °C

Rate of enolisation (liter/mole, sec.): 1.77 X 10-6 Rate of oxidation (liter/mole, sec.): 15.2 x 10-6 pyrophosphate thus involving enolisation as the ion concentrations and from the rate laws. These rate limiting step. This is further substantiated by rates were, then, used to evaluate the rate of the fact that non-enolisable aldehydes like formal­ enolisation under conditions of oxidation of dehyde and chloral do not react with Mn(IlI)- acetaldehyde by Mn(III) sulphate. The rates of pyrophosphate. Thus the rate of oxidation of oxidation and enolisation are recorded in Table VI. aldehydes by Mn(III)-pyrophosphate should give The fact that the rate of oxidation is greater than the rates of enolisation. The rate of enolisation was the rate of enolisation suggests that oxidation of the estimated by measuring the rate of oxidation by aldehyde by Mn(III)-sulphate involves a direct Mn(III)-pyrophosphate at different initial hydrogen attack as shown: HaC H£> c= 0 + Mn(HS04)*3- C=0->Mn(0H)3(HS04)ij' / H H H OH H \/ C H-C. H XC = 0->Mn(0H)2(HS04)3- -* C=0 + Mn(0H)2(HS04)3- + H20 H H I'oof H2C-CH = 0 + Mn(III) + H Q > HCHO + HCOOH + Mn(II)

From the work of K e m p and W a t e r s (1. c.2) the rate Under the acid conditions used here sulphuric acid of oxidation of formaldehyde is 300 times slower exists as HSO 7. Presuming the coordination number than that of acetaldehyde. Formic acid reacts even of Mn(III) to be six, the probable composition could slower than formaldehyde. The presence of formal­ be M n(HS04)2(0H)jj- (cf. Ce(lV) complex). dehyde is, therefore, not unexpected. NOTIZEN 693

1 A. Y. D r u m m o n d and W . A. W a t e r s , J. Chem. ganic Analysis’, p. 327, Longmans Green & Co., Soc. 1953, 435. London 1964. 2 T. J.K e m p and W . A. W a t e r s , ibid. 1964, 339. 5 G. Fiegel, “Spot Tests in Organic Analysis”, p. 435, 3 J. S. L i t t l e r , i b i d . 1962, 832. Elsevier Publishing Co., Amsterdam 1966. 4 A. I. V o g e l , ‘A Text Book of Quantitative Inor­

1,2-Benzthiazolinone: Reaction with Sulphite, Experimental Cyanide, and Cyanate Reaction with N all SO s A mixture of 1 (R=H) (4 g) and aqueous W. V. F a r r a r NaHS03 (30%: 25 ml) was stirred at 50 °C until UMIST, Manchester M60 1QD, England solution was complete. On cooling to 0 °C the so­ dium salt (3, R = S03Na) (5 g) crystallised (plate­ (Z. Naturforsch. 29b, 693-694 [1974]; received June 18, 1974) lets from ethanol). 1,2-Benzthiazolinone, Bing enlargement Analysis (C7H6NNa04S2 • H,0) Found C 31.1 H 3.2 Na 8.6 S 24.0, Reactions of title compound with sulphite, cyanide, Calcd C 30.8 H 2.95 Na 8.4 S 23.45. and cyanate are described. Reaction with cyanide 1,2-Benzthiazolinone (1, R = H ) is a heterocycle When 1 (R = H) was refluxed with aqueous- which undergoes many unexpected reactions. The ethanolic KCN, two isomeric compounds were following have not previously been described. formed; one crystallised directly from the reaction 1 (R = H ) dissolves in aqueous NaHS03 to give mixture, the other was obtained by adding water to an addition compound, at first thought to be the the filtrate. The latter was identical with the sub­ Bunte salt (2, R = S03Na) (cf.1). This reacted as stance precipitated when the „bisulphite compound“ expected with cyanide ion to precipitate a substance (above) was treated with aqueous KCN. 3 (R = CN) which should have been the thiocyanato-compound formed slender needles from aqueous ethanol, (2, R=CN). This could not be so, however, since m.p. ca. 145 °C apparently accompanied by disso­ the supposed 2 (R = CN) was soluble in aqueous ciation into 1 (R = H ) and HCN. alkali and reprecipitated unchanged by acid; only Analysis (C8H6N2OS) the structures 3, (R = S03Na) and 3 (R = CN) will Found C 54.0 H 3.5 N 15.4 S 17.5, account for this fact. It may be that some reactions Calcd C 53.95 H 3.4 N 15.75 S 18.0. of 3-isothiazolone1 will need to be re-interpreted in the light of this result. 3 (R=CN) was soluble in 2 n NaOH, and un­ Reaction of 1 (R = H ) with cyanide gave 3 (R = CN) changed by boiling for 1 h ; similar treatment with directly, accompanied by variable amounts of a high­ 2 N HC1 gave a neutral substance, m.p. 100-102 °C, er-melting isomer; this could be obtained from pure 3 identified as diphenyl disulphide 2,2'-dinitrile4. (R = C N ) by refluxing in ethanol containing a trace The less soluble isomer (4) formed heavy prisms of KCN. It was shown to be the heterocycle (4) by from much ethanol, m.p. 285-286 °C after changing direct comparison with an authentic sample2*3. to long needles at ca. 260 °C. It did not depress the 1 (R = H) reacts readily with phenyl isocyanate, and m.p. of 4 prepared from cyanamide and o-thiol- less smoothly with KCNO, to give 1 (R=CONHPh) benzoic acid2-3. and 1 (R = CONH2), respectively. This would not be Analysis predicted of a compound containing such an acidic NH group. Found C 53.8 H 3.6 N 15.3 S 18.3. Reaction with RCNO .CONH, When equimolecular amounts of 1 (R = H) and a PhNCO were mixed in toluene solution, heat was evolved and 1 (R = CONHPh) crystallised in high yield as prisms, m.p. 186-188 °C (subl.). Request for reprints should be sent to Dr. W. V. Analysis (Ca4H10N2O2S) F a r r a r , The University of Manchester Institute of Science and Technology, PO Box 88, Manchester Found C 62.7 H 4.0 N 10.3 S 11.2, M 60 1QD, England. Calcd C 62.2 H 3.7 N 10.4 S 11.85.